In networks a service tunnel routed between a pair of end points may be protected by rerouting the service tunnel from a currently used routing path to an alternative routing path when a transmission capacity of the currently used routing path becomes insufficient for the service tunnel. Such rerouting is also referred to as dynamic load sharing or protection switching.
Networks with varying transmission capacity at some network links along the routing path can exhibit capacity degradation or even failure of a link. A microwave network with Adaptive Modulation (AM) is an example of a network intentionally designed for link capacity variations. AM is an abundantly deployed solution, e.g., in telecommunications backhaul networks, since AM is an efficient tool to increase the link capacity by adaptively switching to a higher modulation level, if the decreased availability of the higher modulation level can be tolerated. The links are controlled to harness the higher modulation level as long as a Signal-to-Noise Ratio (SNR) of the link is sufficiently high, and to adapt the modulation level as the SNR declines. For example, if a microwave link is planned to provide approximately 100 Mbps link capacity with 99.999% availability by using a Quadrature Amplitude Modulation with 4 constellation points (4-QAM), the link applies 256-QAM achieving a link capacity of approximately 450 Mbps in case of good radio conditions.
As the above example illustrates, the capacity decrease can be quite significant, potentially impacting data of the service tunnel transmitted via the link so that strict Quality of Service (QoS) requirements (e.g., as to delay, jitter and loss of data packets of the service tunnel) can no longer be fulfilled.
In case of double-connected networks, it is possible to protect the impacted service tunnels using a protection switching mechanism. For example, the International Telecommunication Union (ITU) has defined Ethernet Automatic Protection Switching (ETH-APS) in its Recommendation ITU-T G.8031/Y.1342 of June 2011. When the link has failed or its transmission capacity is reduced due to AM, the loss of Continuity Check Messages (CCMs) triggers the rerouting of the impacted service tunnel. End points of the service tunnel then reroute the service tunnel to the alternative path, which does not contain the failed link. In case of services with strict QoS requirements, the rerouting should be completed within a prescribed minimum time. As an example, certain telecommunications applications require resuming within 50 ms.
However, a lower modulation level does not entail the loss of CCMs so that conventional protection switching is not activated. Furthermore, conventional protection switching does not always lead to fulfillment of prescribed QoS requirements. In some situations there is connectivity between the two end-points, so conventional protection switching mechanisms are not activated, but there is capacity degradation, which results in service degradation. In some other situations, the activated protection switching even worsens service performance. Such situations can be observed in microwave networks in case of heavy rain, and more generally, when a plurality of links is impacted in a correlated manner.